Effect of hypergravity on the mouse basal expression of NGF and BDNF in the retina, visual cortex and geniculate nucleus: correlative aspects with NPY immunoreactivity

Ocular Nerve Growth Factor (NGF) and NGF Eye Drop Application as Paradigms to Investigate NGF Neuroprotective and Reparative Actions

The eye is a central nervous system structure that is uniquely accessible to local treatment. Through the ocular surface, it is possible to access the retina, optic nerve, and brain. Animal models of retina degeneration or optic nerve crush could thus serve as tools to investigate whether and how factors, which are anterogradely or retrogradely transported through the optic nerve, might contribute to activate neuroprotection and eventually regeneration. Among these factors, nerve growth factor (NGF) plays a crucial role during development of the visual system, as well as during the entire life span, and in pathological conditions. The ability of NGF to exert survival and trophic actions on the retina and brain cells when applied intraocularly and topically as eye drops is critically reviewed here, together with the effects of ocular neurotrophins on neuronal pathways influencing body rhythm, cognitions, and behavioral functions. The latest data from animal models and humans are presented, and the mechanism of action of ocularly administered NGF is discussed. NGF eye drops are proposed as an experimental strategy to investigate the role and cellular targets of neurotrophins in the mechanism(s) underlying neurodegeneration/regeneration and their involvement in the regulation of neurological and behavioral dysfunctions.

NGF/anti-VEGF combined exposure protects RCS retinal cells and photoreceptors that underwent a local worsening of inflammation

PURPOSE

Our previous study highlighted the potential nerve growth factor (NGF) effect on damaged photoreceptors from a rat model of spontaneous Retinitis Pigmentosa (RP). Herein, we tested the combined NGF/anti-vascular endothelial growth factor (αVEGF) effect on cultured retinal cells isolated from Royal College of Surgeons (RCS) rats receiving an intravitreal VEGF injection (iv-VEGF) to exacerbate retinal inflammation/neovascularization.

METHODS

RCS (n = 75) rats were equally grouped as untreated (n = 25), iv-saline (single saline intravitreal injection; n = 25) and iv-VEGF (single VEGF intravitreal injection; n = 25). Morphological and biochemical analysis or in vitro stimulations with the biomolecular investigation were carried out on explanted retinas. Isolated retinal cells were treated with NGF and αVEGF, either alone or in combination, for 6 days and cells were harvested for morphological and biomolecular analyses.

RESULTS

Infiltrating inflammatory cells were detected in iv-VEGF exposed RCS retinas, indicative of exacerbated inflammation and neovascularization. In cell cultures, NGF/αVEGF significantly increased retinal cell survival as well as rhodopsin expression and neurite outgrowth in photoreceptors. Particularly, NGF/αVEGF upregulated Bcl-2 mRNA, downregulated Bax mRNA, upregulated trkA^NGFR mRNA and finally upregulated both NGF mRNA and protein.

CONCLUSIONS

These data confirm and extend our previous findings on NGF-photoreceptor crosstalk, highlighting that the NGF/αVEGF combination might be an interesting approach for improving neuroprotection of RCS retinal cells and likewise photoreceptors in the presence of neovascularization. Further studies are required to translate this in vitro approach into clinical practice.

High-flavonoid intake induces cognitive improvements linked to changes in serum brain-derived neurotrophic factor: Two randomised, controlled trials

BACKGROUND: Recent clinical studies have indicated the beneficial impact of dietary flavonoid intake on human cognitive performance. Although the mechanisms that mediate such improvements are currently unclear, animal and human trial data suggest that changes in neurotrophin expression, and related signalling apparatus, may be involved.

OBJECTIVE: To investigate the link between changes in serum brain-derived neurotrophic factor (BDNF) and changes in human cognitive performance following flavonoid intake.

METHODS: The relationship between serum levels of BDNF and age, gender, BMI, waist circumference, blood pressure and cognition at baseline, and following flavonoid intake, was investigated in two distinct randomised, controlled clinical trials. Trial 1 was conducted in men and women (aged 26–70 y; consuming an average of 3 portions of fruit and vegetables per day) and delivered high-flavonoid (>15 mg/100 g) or low-flavonoid (<5 mg/100 g) fruit and vegetables and increased intake by 2 portions every 6 weeks. The control arm was habitual diet over the same time frame. Trial 2 was conducted in an older males and female cohort (aged 62–75 y) intervening with a high-flavanol cocoa drink (494 mg total flavanols) and a low-flavanol cocoa drink (23 mg total flavanols) for 12 weeks.

RESULTS: Serum BDNF levels increased linearly to the age of 65, after which BDNF levels were found to decrease markedly. All other physiological and anthropometric measurements proved to not be significantly associated with serum BDNF levels (p > 0.05), although higher levels in males compared to females almost achieved significance (p = 0.056). At baseline, higher serum BDNF levels were associated with significantly better global cognition scores, relative to individuals with lower serum levels. In addition, following intervention for 18 weeks, high-flavonoid, but not low-flavonoid, fruit and vegetable intake induced significant improvements in cognitive performance and increases in serum BDNF levels (p = <0.001). Flavanol intervention for 12 weeks also resulted in significant increases in serum BDNF (p = <0.001), and such increases were correlated with improvements in global cognitive performance.

CONCLUSION: Increases in global cognition induced by high flavonoid fruit and vegetables, and cocoa flavanols were paralleled by concurrent changes in serum BDNF levels, suggesting a role for BDNF in flavonoid-induced cognitive improvements. Furthermore, we provide further data suggesting that serum BDNF levels may represent a biomarker of cognitive function.

Evaluation of gene, protein and neurotrophin expression in the brain of mice exposed to space environment for 91 days

Effects of 3-month exposure to microgravity environment on the expression of genes and proteins in mouse brain were studied. Moreover, responses of neurobiological parameters, nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF), were also evaluated in the cerebellum, hippocampus, cortex, and adrenal glands. Spaceflight-related changes in gene and protein expression were observed. Biological processes of the up-regulated genes were related to the immune response, metabolic process, and/or inflammatory response. Changes of cellular components involving in microsome and vesicular fraction were also noted. Molecular function categories were related to various enzyme activities. The biological processes in the down-regulated genes were related to various metabolic and catabolic processes. Cellular components were related to cytoplasm and mitochondrion. The down-regulated molecular functions were related to catalytic and oxidoreductase activities. Up-regulation of 28 proteins was seen following spaceflight vs. those in ground control. These proteins were related to mitochondrial metabolism, synthesis and hydrolysis of ATP, calcium/calmodulin metabolism, nervous system, and transport of proteins and/or amino acids. Down-regulated proteins were related to mitochondrial metabolism. Expression of NGF in hippocampus, cortex, and adrenal gland of wild type animal tended to decrease following spaceflight. As for pleiotrophin transgenic mice, spaceflight-related reduction of NGF occured only in adrenal gland. Consistent trends between various portions of brain and adrenal gland were not observed in the responses of BDNF to spaceflight. Although exposure to real microgravity influenced the expression of a number of genes and proteins in the brain that have been shown to be involved in a wide spectrum of biological function, it is still unclear how the functional properties of brain were influenced by 3-month exposure to microgravity.

Effect of exogenous administration of nerve growth factor in the retina of rats with inherited retinitis pigmentosa

NGF is implicated in retinal damage regression. To study whether this is a direct effect or an effect mediated by NGF on other endogenous biological mediators, we investigated the effect of exogenous administration of NGF in RCS rats affected by retinitis pigmentosa. We found that NGF administration exerts a rescue effect on photoreceptors in this animal model. NGF injection enhances brain-derived neurotrophic factor, beta-fibroblast growth factor, transforming growth factor-beta, vascular endothelial factor and neuropeptide-Y. This suggests that NGF has an effect on RCS rat retina, probably also through the stimulation of other biological mediators produced and released in the retina.

Effects of a 14-day period of hindpaw sensory restriction on mRNA and protein levels of NGF and BDNF in the hindpaw primary somatosensory cortex

Neurotrophins have been reported to play an important role in neuronal plasticity and to be regulated by neuronal activity and/or neurotransmitters. Recently, we have shown that hindpaw sensory restriction induces a cortical reorganisation in the hindpaw primary somatosensory cortex, and that acetylcholine plays a significant role in this process. Sensory restriction was obtained by hindlimb suspension for 14 days. In this study, we examined the effects of a long period of hindpaw sensory restriction on the NGF and BDNF mRNA and protein expressions in the hindpaw somatosensory cortex. mRNA and protein levels were assessed by RT-PCR and ELISA, respectively. First, we found that NGF and BDNF mRNA relative levels increased after hindpaw sensory restriction. Second, the level of NGF protein increased, whereas that of BDNF remained unchanged. This differential response of NGF and BDNF proteins to sensory restriction suggested different levels of gene regulation, i.e., at pretranslational or posttranslational states. Moreover, inasmuch as our results differ from other models of sensory restriction (dark rearing, whisker removal, etc.), we hypothesized that the regulation of neurotrophin expression is dependent on the type and duration of the sensory restriction. In conclusion, we argue that neuronal plasticity induced by hindpaw sensory restriction requires neurotrophin expression.

Neurobehavioral coping to altered gravity: endogenous responses of neurotrophins

An altered gravitational environment represents a unique challenge for biological systems that have evolved against gravitational background. Ground-based and space research indicates that the developing nervous system is potentially affected by exposure to hyper/microgravity. With the construction of the orbiting International Space Station long-term research on the nervous system will be possible. With this perspective, we started ground-based studies to characterize mouse behavioral responses to rotation-induced 2 g hypergravity, using a custom-made centrifuge device. Brain levels of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) as well as NGF and BDNF expression and mast cell distribution in heart and lung, were evaluated and correlated with the changes in mouse behavior upon hypergravity exposure. Hypergravity strongly affected the spontaneous activity of the animals, selectively modifying mouse behavioral repertoire. Such changes were mainly related to variations in brain levels of NGF, while BDNF was slightly affected, thus confirming a role for these neurotrophins in neuronal plasticity underlying experience-induced neurobehavioral changes. Moreover, gender differences were observed in both behavioral and neurobiological responses to hypergravity. These results indicate that changes in the gravitational environment might represent a useful tool to investigate the neurobiological and behavioral responses to stressors and may provide insights into the mechanisms underlying development and plasticity of nervous system in brain, heart, and lung.

Exploration and motor activity in juvenile and adult rats exposed to hypergravity at 1.8 G during development: a preliminary report

Pups from gestating rats exposed to hypergravity (1.8 G) or to normal gravity at the perinatal period were evaluated for motor activity, exploration and social interactions during juvenile and adult stages. By comparison to controls, the hypergravity group had shorter latencies before choosing a maze arm in a T-maze and a lower number of exploratory pokes in a hole board. During dyadic encounters, the hypergravity group had a lower number of self-grooming episodes and shorter latencies before crossing under the opposing rat. In contrast, no intergroup differences were observed during exploration of an elevated plus-maze and a light-dark box. These results indicate that exposure to 1.8 G during development appears to decrease exploratory tendencies in the hole board and fear-related responses in T-maze and social interaction tests.

Stress and nerve growth factor: findings in animal models and humans

Stress is elicited by environmental, social or pathological conditions occurring during the life of animals and humans that determine changes in the nervous, endocrine and immune systems. In the present review, we present data supporting the hypothesis that stress-related events both in animal models and humans are characterized by modifications of endogenous nerve growth factor (NGF) synthesis and/or utilization. Stress inducing alteration in NGF synthesis and/or utilization appears to be more severe during neurogenesis and in early postnatal life. However, NGF endogenously released during stress may promote remodeling of damaged tissues following acute and/or chronic stressful events.